The present invention is directed to tamper-evident, pressure sensitive facestock labels which are useful on a wide variety of substrates including for example, stainless steel, aluminum, paper paper-like products and plastics, such as polyethylene.
Pressure sensitive labels consist basically of three components: a release liner, a pressure sensitive adhesive and a facestock material or actual label. The facestock label is printed on one side with the intended decoration design or message, while the opposite side of the label is coated with the designated pressure sensitive adhesive material. The function of the release liner is to protect the adhesive, act as a die-cutting base and carry the face stock label through a converting process. Pressure sensitive labels are subjected to various converting processes or steps during their manufacture and use. The major converting processes include (1) coating one side of the release liner with a pressure sensitive adhesive, (2) laminating the release liner to the facestock material, (3) printing on the facestock side of the label, (4) die-cutting the facestock material, and (5) applying the facestock label to the surface of an end use product, often known as label dispensing and application.
There have been many efforts to provide tamper-evident materials for application to packages for pharmaceutical and foodstuff products. In addition, various types of labels disintegrate or show evidence of tampering if the label is removed from the substrate.
The U.S. Pat. No. 5,013,088 to Marin discloses disintegratable masking labels which have a plurality of cuts in the label such that upon tampering, portions of the label remain bonded to the substrate and the remaining label fragments show evidence of tampering of the label.
The U.S. Pat. No. 4,931,327 to Liu et al. discloses a tamper evident film comprising a core layer and at least one oriented tamper-evident layer applied to the core layer. The tamper-evident layer comprises a mixture of a polyolefin and filler or particles which induce cavitation upon orientation of the film. An oriented skin layer is applied to the core layer if tamper-evident layers have not previously been applied to both sides of the core layer.
The U.S. Pat. No. 4,876,123 to Rivera et al. discloses a tamper indicating tape including a delaminating film which delaminates internally between first and second major surfaces. The tamper indicating tape also includes colored indicia printed on the major surfaces of the film and an adhesive means for adhering the film to a substrate.
The U.S. Pat. No. 4,121,003 to Williams discloses tamper indicating labels comprising a laminate of a transparent outer sheet having a tamper-indicated, information-containing pattern printed on its inner surface and a pressure sensitive adhesive film coated on the printed inner surface of the outer sheet.
In addition, various types of tamper-evident labels are made from polyvinylchloride and cellulose acetate materials. Typically, these tamper-evident films are made using a solution casting process. The solution casting of polyvinylchloride and/or cellulose acetate film is expensive and complicated and requires extensive handling of the solvent. A polyvinychloride and/or cellulose acetate material is dissolved in a suitable solvent and thereafter spread out over drums, belts, coated papers or the like to evaporate the solvents. Upon evaporation of the solvent, the solute loses its flexibility and eventually becomes very rigid and brittle. The rigid, brittle material is easily susceptible to destruction if any external mechanical stresses are exerted.
Until the present invention it has not been possible to use melt extrusion processes, blown or cast, for producing brittle type films. In a typical cast extrusion process the film undergoes tension and stress and is subject to movement and vibrations of the processing equipment which causes the film to shatter or fracture.
Therefore, it is an object of the present invention to provide a tamper-evident pressure sensitive coated facestock label which provides visible evidence that tampering has occurred.
It is a further object of the present invention to provide tamper-evident pressure sensitive coated facestock labels which can be applied on diverse types of substrates such as metals, plastics, paper, paper-like products and the like.
It is still a further object of the present invention to provide a tamper-evident pressure sensitive coated facestock label which readily disintegrates upon removal of the label from a substrate.
It is an additional object of the present invention to provide a tamper-evident pressure sensitive label which does not involve the use of solvents during the manufacturing process of the label.
It is an additional object of the present invention to provide a tamper-evident pressure sensitive label which can be produced using a cast extrusion process.
It is still an additional object of the present invention to provide a method for producing a tamper-evident pressure sensitive label by cast extrusion.